SHARP stone flakes found two decades ago in a parched riverbed in the Afar region of Ethiopia are the oldest tools yet discovered. They date from 2.6 million years ago. It would be another million years before our ancestors made their next technological breakthrough. Then, instead of using the chips off a river cobble as blades and scrapers, someone realised that the cobble itself could be worked into a tool. “It is recognisable as a hand axe, but very rough,” says Dietrich Stout of Emory University, Atlanta. Another million years passed before early modern humans perfected this technique. What took them so long?

Intelligence must have played a part. In the 2 million years after the appearance of the first tools, hominin brain size more than doubled, to around 900 cubic centimetres. Toolmaking undoubtedly requires smarts, and Stout has used MRI scans of people knapping stones to find out which brain areas are involved. The studies suggest that early technological innovations depended on novel perceptual-motor capabilities – such as the ability to control joint stiffness – while later developments were underpinned by growing cognitive complexity, including the sort of recursive thinking required for language (PLoS One, vol 5, e13718). So, although tools appear not to develop much, their production is underpinned by great cognitive advance, leading Stout to conclude that there was more progress during this period than we tend to think. What’s more, he says, people may have made other tools from …